"When Mitscherlich discovered that Glauber's salt gave a definite pressure of water vapor, he at once formed the hypothesis, that is, supposition, that other hydrates would be found to do likewise. Experiments showed this supposition to be correct. The hypothesis was at once displaced by the fact. This sort of hypothesis predicts the probable existence of certain facts or connections of facts; hence, reviving a disused word, we call it a stochastic hypothesis (Greek στοχαστικός, apt to divine the truth by conjecture). It differs from the other kind in that it professes to be composed entirely of verifiable facts and is subjected to verification as quickly as possible."
Alexander Smith. Inorganic Chemistry. 1909.

"I think that it is very interesting that one can see the [psi] functions of Schrödinger’s wave mechanics by means of the X-ray study of crystals. This work should be continued experimentally. I believe that much information regarding the nature of the chemical bond will result from it."
Linus Pauling. Letter to A. A. Noyes. 1926.

"My wife and I think of you often. Our favorite daydream has for its theme a visit to Manchester."
Linus Pauling. Letter to William Lawrence Bragg. March 8, 1928.

"I am enclosing a copy of a manuscript which Mr. Sturdivant and I have prepared, dealing with the structure of brookite. We feel rather confident in our structure, and are pleased to have begun work in the field which you recently opened -- the study of complex ionic crystals."
Linus Pauling. Letter to William Lawrence Bragg. May 31, 1928.

"...[T]o awaken an interest in chemistry in students we mustn’t make the courses consist entirely of explanations, forgetting to mention what there is to be explained."
Linus Pauling. Letter to A. A. Noyes. November 18, 1930.

"Even the formal justification of the electron-pair bond in the simplest cases...requires a formidable array of symbols and equations."
Linus Pauling. "The nature of the chemical bond. Application of results obtained from the quantum mechanics and from a theory of paramagnetic susceptibility to the structure of molecules." J. Am. Chem. Soc. 53 (April 1931): 1367-1400. 1931.

"I consider that the field of work in which Dr. Pauling is engaged, namely the study of the chemical bond and of valence from the standpoint of modern physics, is the most important line of research in theoretical chemistry today; and I venture to believe that there is no one in the world who in the same degree has chemical background and at the same time has the physical knowledge, mathematical power, and originality required for the handling of this problem."
A. A. Noyes. Letter to William Foster. October 15, 1931.

"Attempts to regard a molecule as consisting of specific atoms or ionic units held together by discrete numbers of bonding electrons or electron pairs are considered as more or less meaningless."
Robert Mulliken. Selected Papers of Robert S. Mulliken, D.A. Ramsay and J. Hinze, eds., p. 451. 1932.

"I should like to do some work (with Professor Yost) in an attempt to prepare certain compounds of xenon suggested by theoretical arguments. No doubt your xenon is precious; if, however, you could lend us 10 cc or so (of not necessarily pure stuff), we would try to return it to you either as such or in some compound (I hope), and we would be properly grateful."
Linus Pauling. Letter to Fred Allen. September 13, 1932.

[Pauling] has a speculative mind of the first order, great analytical ability, and the genius to keep in close and inspiring touch with experimental work.... He...is nearly universally rated as the leading theoretical chemist of the world.
Warren Weaver. Weaver diary notes, as referenced in Force of Nature, by Tom Hager, p. 187. October 1933.

"I have just returned from a short vacation for which the only books I took were a half-dozen detective stories and your 'Chemical Bond'. I found yours the most exciting of the lot."
G.N. Lewis. Letter to Linus Pauling. August 25, 1939.

"I have been very much interested by your new book and have assigned several of the chapters for reading in connection with a graduate course. As evidence of my interest in it I can cite the fact that it is the first scientific book which I can remember reading during the course of a fishing trip, although I have carried many with me in the past."
Charles P. Smyth. Letter to Linus Pauling. December 15, 1939.

"Just recently we have been having an unusually large sale of the book. This morning, for instance, we received a cablegram from Japan for 100 copies. Our stock in this country is now below 1,000 and we must arrange for a new printing or a new edition."
W.S. Schaefer. Letter to Linus Pauling. July 15, 1941.

"Dr. Linus Pauling is the man for me / He makes violent changes in my chemistry / Oh, fie, when he rolls his eyes / All my atoms ionize."
Chemistry-Biology Stock Company, C.I.T.. Song lyrics from "The Road to Stockholm." 1954.

"I doubt that many Nobel Prizes have been so popular with the masses in science.... [A]lmost all are delighted that the Nobel Prize embarrasses the State Department."
Charles Coryell. Letter to J. Robert Oppenheimer, as referenced in Force of Nature, by Tom Hager, p. 451. November 2, 1954.

"I slept till very late in the morning, found I couldn’t do work at all, had a quick lunch, went to sleep again in the afternoon and slept until five o’clock. When I woke up...I had clearly...the picture before me of the two wave functions of two hydrogen molecules joined together with a plus and minus and with the exchange in it. So I was very excited, and I got up and thought it out. As soon as I was clear that the exchange did play a role, I called London up, and he came to me as quickly as possible. Meanwhile I had already started developing a sort of perturbation theory. We worked together then until rather late at night, and then by that time most of the paper was clear.... Well...at least it was not later than the following day that we had the formation of the hydrogen molecule in our hands, and we also knew that there was a second mode of interaction which meant repulsion between two hydrogen atoms, also new at the time –- new to chemists, too."
Walter Heitler. AHQP (Archive for the History of Quantum Physics), volume 6. March 18, 1963.

"I can remember that I was asked, perhaps when I was a junior, if I would give some lectures in the evening for students who were having trouble in freshman chemistry . . . I can remember presenting chemical bond theory on the 'hook-and-eye' basis . . . [When] I ran across the papers by Langmuir which were published that year . . . I was very impressed by this work on the electronic structure of molecules or ideas about shared electron pair bonds, and it may well be that that was the start of my interest in chemical bonding."
Linus Pauling. Interview by John Heilbron, in Linus Pauling: A Man and His Science, by Anthony Serafini. 1964.

"When I was in Europe...I received a letter from A. A. Noyes saying that he was writing to offer me an appointment as 'Assistant Professor of Theoretical Chemistry and Mathematical Physics,' and I accepted it, but by the time that I got here it had been changed to 'Assistant Professor of Theoretical Chemistry' . . . I don't know what happened with the physics, whether Millikan objected to my having a joint appointment or whether Noyes decided . . . [Noyes] was preventing me from going to Berkeley, and he may have decided that he didn't want me associated with the physics department in this way, that perhaps I would shift."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"At Berkeley and at Pasadena, the chemists, the physical chemists, were learning as much physics and mathematics as the physicists did and they were able to take advantage of this opportunity in the way that European chemists were not."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"Goudsmit and I were never together, I think, during the period when [The Structure of Line Spectra] was written. He would write a draft of some material that he thought ought to go in the book and then using that as a basis I wrote the corresponding sections of the book."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"[P.W.] Bridgman . . . would say that a question that does not have operational significance, that does not lead to an experiment of some sort, or an observation, it's significant. I never have been bothered by the detailed or penetrating discussions about interpretation of quantum mechanics."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"The department of chemistry [at Harvard] seemed to me to be rather uncooperative in that the different professors ran their own little groups...I just thought that I wouldn't feel at home there...."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"One day, late in the day...I had an idea. It was the basic idea of hybrid orbitals. I was trying to understand why the carbon atom is tetrahedral, forms bonds directed towards the four corners of a tetrahedron. Even as early as 1924, I had made a model of methane, in which I said the four outer electrons of the carbon are in orbits directed towards the corners of a tetrahedron.... When quantum mechanics came along, a result was confirmed that had been accepted earlier, that the four outer electrons in the carbon are of two different kinds.... I thought 'the basic principles of quantum mechanics permit us to combine these functions from the Schrödinger equation in another way.' And I said to myself: 'Let’s suppose that I look just at the distribution in various directions, and not worry about the difference in the radial distribution for those.' This permitted rather simple calculations to be made in a straightforward manner. The first result I got was that the best bonds that the carbon atom can form are directed towards the four corners of a tetrahedron. So, in 1931, I had a simple theory of the tetrahedral carbon atom and an explanation of a great bit of organic chemistry."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), volume 6. March 27, 1964.

"There was this long gap from 1928 when I wrote my first paper on quantum mechanics of the chemical bond in the Proceedings of the Royal Society, and 1931 when I wrote the first significant paper. Well, there was this gap because I was having so much trouble getting a result that was in simple enough form to be valuable to chemists and to have more significance than numbers that you would get out of a computer nowadays."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"I was just as pleased to be Assistant Professor of Theoretical Chemistry but pretty soon, when I became Professor in 1931, I said I wanted to have the title of Professor of Chemistry -- not theoretical chemistry...not physical chemistry...just Professor of Chemistry."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"We had to have the ideas about partial ionic character of covalent bonds, you know, which I developed in about ’33, ’32, before it became possible to discuss electro-neutrality in a very significant way."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"I published a paper with Jack Sherman on the calculation of some of these overlap integrals with a simplification.... It's in The Nature of the Chemical Bond, the results are -- with a simplification of some sort; it's like taking Slater functions, I don't know what it was, but actually evaluating the overlap integrals. Our conclusion was that the bond strength function giving angular dependence alone is really pretty good -- not perfect but pretty good."
Linus Pauling. AHQP (Archive for the History of Quantum Physics), interview transcript part 2. Interview by John Heilbron. March 27, 1964.

"Even when being asked questions about some serious matter [Oppenheimer] likes to answer in devious and sybilline fashion; but after a few such excursions his bewildered hearer is astonished to find that the answer as a whole, so far from evading the question, has illuminated it in depth by means of some brilliant, unexpected perception which reveals hitherto unnoticed relationships."
Michel Rouze. Robert Oppenheimer, The Man and His Theories. 1965.

"The theory of quantum mechanical resonance of molecules among several valence-bond structures constituted a major addition to the classical structure of organic chemistry. This theory was developed in the period from 1931 on by a number of investigators including Slater, E. Huckel, G. W. Wheland and me."
Linus Pauling. "Fifty years of progress in structural chemistry and molecular biology," Daedalus, 99 (Fall 1970): 988-1014. 1970.

"I remember clearly how much different my own thinking about molecular structure and the chemical bond was in 1935 from what it had been ten years earlier. In 1925...I had no way of distinguishing between the good ideas and the poor ideas about the electronic structure of molecules."
Linus Pauling. "Fifty years of progress in structural chemistry and molecular biology," Daedalus, 99 (Fall 1970): 988-1014. 1970.

"By 1935...I felt that I had an essentially complete understanding of the nature of the chemical bond."
Linus Pauling. "Fifty years of progress in structural chemistry and molecular biology," Daedalus, 99 (Fall 1970): 988-1014. 1970.

"Just as evolution is inseparably connected with Darwin (and not with Wallace, whose paper on evolution prompted Darwin to write The Origin of Species), so too Pauling and the chemical bond are tightly associated, and Slater's position, though important, is secondary and supportive."
Robert J. Paradowski. The Structural Chemistry of Linus Pauling, pg. 333. 1972.

"Pauling's paper on bond energy and electronegativity proved to be highly influential. The qualitative concept of electronegativity as the ability of an atom in a molecule to attract electrons to itself was an old one. Early in the twentieth century, it was associated in a crude way with the metallic or non-metallic character of an element, or with its place in the activity series of the metals. The importance of Pauling's paper derives from the fact that he was the first person to put this property on a numerical basis."
Robert J. Paradowski. The Structural Chemistry of Linus Pauling, pg. 450. 1972.

"For Schrödinger, the atom was an oscillating system -- like the string of a musical instrument -- for which there exist a number of modes of oscillation (fundamentals and overtones) which are interpreted as the atom's energy states. Schrödinger's wave equation impressively provided -- without any additional assumptions -- the right values for spectral lines of the hydrogen atom."
Armin Hermann. Werner Heisenberg 1901-1976, pg. 36. 1976.

"In 1931 when my papers on the nature of the chemical bond appeared, Professor Noyes, who was chairman of the Division of Chemistry and Chemical Engineering, said that I probably would get the Nobel Prize someday. Well, I thought, that's nice of the old guy to say that, but I'm a little skeptical myself. And as the years went by, I thought, I don't do the sort of work for which Nobel Prizes are given."
Linus Pauling. NOVA Interview. 1977.

"I'd begun to think about the theory of the chemical bond very seriously in 1926, '27, after quantum mechanics was discovered and then in 1928 I published a paper, a preliminary paper, and said that I would write more later on. I didn't write anything more for three years because the problem turned out to be such a hard problem, the mathematical problem, that I couldn't solve it."
Linus Pauling. NOVA Interview. 1977.

"It seems to me that I have introduced into my work on the chemical bond a way of thinking that might not have been introduced by anyone else, at least not for quite a while. I suppose that the complex of ideas that I originated in the period of around 1928 to 1933 -- and 1931 was probably my most important paper -- has had the greatest impact on chemistry."
Linus Pauling. NOVA Interview. 1977.

"Heisenberg has discussed the coupled double harmonic oscillator, and has shown that the ordinary rules of quantization lead to two non-combining sets of states in one of which the electrons are in phase and out of phase. The energy of the system is successively transferred from one to the other -- resonance!"
Linus Pauling. NOVA Interview. 1977.

"I think my work on the chemical bond probably has been most important in changing the activities of chemists all over the world -- changing their ways of thinking and affecting the progress of the science."
Linus Pauling. NOVA Interview. 1977.

"For five years, beginning in spring 1929, I spent one or two months each year in Berkeley as a visiting lecturer in physics and chemistry. During these extended visits to Berkeley I had the pleasure of talking with [G.N.] Lewis for many hours, in his office, his home, and in his Marin County country place."
Linus Pauling. "Pauling on G.N. Lewis," Chemtech 13 (June 1983): 334-337. 1983.

"One could say that Pauling's 'failure' was to plant a lot of seeds, basic ideas, without working them out fully.... As soon as Slater gets an idea he works it out to the end before he gets a new one. But that is also dangerous, of course because you look at the trees and you don't see the forest...[Pauling] looks at the forest and lets other people...work out the specific individual things in detail; he has a terrifically lively intellect, reading [Pauling's] paper, the information here is just tremendous, the ideas flow out of the pen, and there are several lifetimes of work...to be done."
Sten Samson. Interviewed by Anthony Serafini for Linus Pauling: A Man and His Science. 1984.

"Einstein came over here and attended a scientific meeting and at the end of the meeting Pauling was to deliver a paper; Pauling was introduced and delivered a paper in flawless German! And after meeting him, Einstein congratulated him and asked him, 'Where did you learn to speak such flawless German?' And Pauling said, 'Oh, I spent a year in Germany' and Einstein said, 'You learned to speak German in a year like that? Why I've been here over two years and I can't speak English yet!'
W. K. Ferrier. Interviewed by Anthony Serafini for Linus Pauling: A Man and His Science. 1984.

"The paper of Heitler and London on H₂ for the first time seemed to provide a basic understanding, which could be extended to other molecules. Linus Pauling at the California Institute of Technology in Pasadena soon used the valence bond method. . . . As a master salesman and showman, Linus persuaded chemists all over the world to think of typical molecular structures in terms of the valence bond method."
Robert Mulliken. Life of a Scientist, pp. 60-61. 1989.

"Pasadena at that time seemed an earthly paradise, with good science too. We had a dip in the Pacific Ocean at Christmas [1935]. Although Pauling and I were at that time rivals on the subject of valence bond theory, we had friendly relations with the Pauling family: Linus and Ava Helen one day took us for a memorable expedition into the desert."
Robert Mulliken. Life of a Scientist, pg. 97. 1989.

"I had something of a shock when I went to Europe in 1926 and discovered that there were a good number of people around that I thought to be smarter than me."
Linus Pauling. Interview with Tom Hager, published in Force of Nature, p. 130. 1991.

"Anybody could see that quantum mechanics must lead to the tetrahedral carbon atom, because we have it. But the equations were so complicated that I never could be sure that I could present the arguments in such a way that they would be convincing to anybody."
Linus Pauling. Interview with Tom Hager, published in Force of Nature, p. 142. 1991.

"My attitude was, why shouldn’t I use the understanding that I have developed of the nature of crystals in inorganic substances to proceed to predict their structures?"
Linus Pauling. Interview with Tom Hager, published in Force of Nature, p. 144. 1991.

"I might well have become egotistical as a result [of the Langmuir Prize].... But...I think that I just said I shouldn’t let this go to my head. I shouldn’t think I’m really better than other people even though I do this one thing better than other people."
Linus Pauling. Interview with Tom Hager, published in Force of Nature, p. 160. 1991.

"I had become interested in the question of the nature of the chemical bond, after having read the 1916 paper on the shared-electron-pair chemical bond by G.N. Lewis and the several 1919 and 1920 papers by Irving Langmuir on this subject."
Linus Pauling. The Chemical Bond: Structure of Dynamics, Ahmed Zewail, ed. 1992.

"My year in Munich was very productive. I not only got a very good grasp of quantum mechanics -- by attending Sommerfeld's lectures on the subject, as well as other lectures by him and other people in the University, and also by my own study of published papers -- but in addition I was able to begin attacking many problems dealing with the nature of the chemical bond by applying quantum mechanics to these problems."
Linus Pauling. The Chemical Bond: Structure of Dynamics, Ahmed Zewail, ed. 1992.

"I consider my entry into the field of x-ray crystallography, nine years after it had been developed, to be just about the most fortunate accident that I have experienced in my life."
Linus Pauling. The Chemical Bond: Structure of Dynamics, Ahmed Zewail, ed. 1992.